In several fields it has been found desirable to use hydraulic motors for driving certain mechanisms. One such field is the field of Oral Hygiene. In this field, hydraulic motors are superior to electric motors because (1) they can be made out of non-conductive/non-magnetic light materials such as plastics, (2) they do not represent an electric shock hazzard, and (3) they are quieter. Such hydraulic motors, such as the ones described by U.S. Pat. Nos. 3,536,065, 3,489,885, and 3,524,208 comprise an expansible-chamber hydraulic motor "driven by liquid pulses of a liquid through a flexible pipe; said pulses being introduced into the pipe by an appropriate liquid pulse generator. Usually after it expands its energy, the liquid is returned to the source by a separate pipe. However, it has been found in general that such arrangements are very inefficient because the flexible pipes dampen the liquid pulses very drastically and thus the power transmission through these pipes is very poor and unpredictable.